The present invention relates to a sensor assembly for electrochemical analysis of a substance, its method of use and its major constituative components, and more particularly, concerns a sensor assembly for blood gas analysis at the bedside of a patient, its method of use and major constituative components.
2. Description of the Prior Art
Blood gas analysis has been performed on arterial blood of patients, particularly those with a critical illness, to determine the acid base and blood gas condition of these patients in assessing overall homeostasis. In particular, arterial pH, pO.sub.2 and pCO.sub.2 are measured from a sample of arterial blood to determine the biochemical status of the patient's blood. In accordance with conventional techniques for arterial blood gas analysis, the therapist responsible for obtaining the sample generally starts the procedure with an arterial blood gas kit dispensed from a central location (nursing station or lab). This blood gas kit is then brought to the bedside of the patient and opened. A bag is normally provided within each kit for ice, or a suitable container may be used. The bag or container is filled with a slurry of crushed ice and water and brought to the patient's room. A syringe is taken from the arterial blood gas kit and appropriately labeled according to standard practice. The inside of the syringe is normally coated with heparin at bedside, and excess heparin is expelled from the syringe by pushing the plunger inwardly until it stops. A small amount of heparin usually remains within the syringe which prevents the blood sample from clotting.
At this time, the therapist locates the patient's artery, preps the site with alcohol or the like and inserts the syringe needle into the artery. Arterial pressure forces blood into the syringe until it is filled to the desired level whereupon the therapist removes the needle from the patient and suitably caps it. The patient now requires pressure held on the site of the artery for a period of about five minutes until the bleeding stops. Air remaining in the syringe is removed, and the syringe is normally rolled between the therapist's hands to assure a complete mixing of the heparin, whereupon the filled syringe is placed in the container of ice. From the patient's bedside, the sample of blood is transported to the laboratory where it is analyzed.
In the laboratory, the sample is taken to the blood gas analyzer, rolled between the therapist's hands again to be sure it is thoroughly mixed, and injected into the analyzer. After a period of one to two minutes, the analysis is completed and either transcribed in writing by the operator of the analyzer or printed thereby. The results of this analysis are then brought back for listing on the patient's bedside chart. In addition, the patient's doctor is normally notified of these results. In normal, conventional blood gas analyses as described above, the average time from syringe preparation to the printout of the final results is about twenty minutes. Moreover, it has been estimated that as much as thirty percent (30%) to fifty percent (50%) of a respiratory therapy department's staffing may be involved in arterial blood gas procedures.
It can be seen that improvements in time and personpower in arterial blood gas analysis are desirable. Transportation of the arterial blood gas sample to a remote, central lab not only takes time, but could introduce errors or inaccuracies in the final analysis if the sample has not been treated properly. Furthermore, inasmuch as the blood gas sample must literally be transferred into the central processing unit from the original arterial syringe, the entire procedure is subjected to even more inaccuracies or opportunities for error.
As is evident from the above description, it would be most desirable to be able to perform the arterial blood gas analysis at the patient's bedside, i.e., the measurements of blood pH, pO.sub.2 and pCO.sub.2, and perhaps other blood information, would be available to the therapist immediately without having to transport the sample to a remote, central laboratory. One of the problems associated with such a proposed bedside technique, of course, involves equipment expense and perhaps a multiplicity of units which may not read uniformly. However, state of the art technology and carefully prepared calibration techniques are available to minimize equipment expense and assure that bedside blood gas analysis equipment will make substantially uniform and reproducible measurements. Another problem for such a proposed bedside technique involves the sensing devices to sense pH, pO.sub.2 and pCO.sub.2. A viable technique has been heretofore unknown which would allow the electrochemical analysis of blood pH, pO.sub.2 and pCO.sub.2 in a portable sensing device wherein the electrodes do not have to be cleaned after each use, which is normally performed on the electrodes of centrally located blood gas analyzers. While transcutaneous electrodes are known and available for measuring certain blood gases, it is believed that such transcutaneous electrodes do not measure the transfer of ions thereacross which would be necessary in measuring pH values. A sensor for electrochemical analysis has recently been described in U.S. Pat. No. 4,197,582, which is described as capable of measuring blood gases and ions. However, the sensor of the aforementioned patent is intended for in vivo measurements in a precisely predeterminable location in the living body.
Therefore, the present invention is directed to overcoming the problematical areas set forth above while at the same time achieving the desirable aims of a bedside or portable blood gas analyzer and procedure.